There are already known various constructions of aircraft flight control systems, among them such in which the flight regime of an aircraft, such as a helicopter, is controlled by a flight control computer in response to various inputs, including those representing pilot commands resulting, for instance, from manipulation of a collective stick, a switch or the like by a pilot. Examples of control systems of this type can be found, for instance, in U.S. Pat. Nos. 3,743,221, 3,945,590, 4,114,842, 4,642,774 and 4,765,141, to which reference may be had for details of the construction and operation of aircraft equipped with such flight control computers and the manner in which such control systems of this kind are modified to respond to various types of contingencies or to perform desired aircraft maneuvers.
Operating a helicopter is a very demanding activity for the pilot, especially when the helicopter is to be used in military operations where the pilot, besides attending to routine flight control tasks, has to devote his attention to a multitude of other tasks, such as evaluating the battlefield situation based on visual observation and/or instrument reading, monitoring and operating various weapons systems, evading perceived or actual threats from enemy action, and the like.
To minimize the capability of the enemy to detect the aircraft and/or engage it with lethal weapons, a technique which is often resorted to is so-called nap-of-the-earth flight where the pilot utilizes the features of the battlefield terrain and ground cover to hide behind. While this technique minimizes the risk that the helicopter would be spotted or detected by enemy forces and that, as a result, it would be subjected to hostile action by the enemy, such a covert operation technique, by the same token, limits the ability of the pilot or other crew of the helicopter to observe, detect, evaluate, and take action against, potential enemy targets.
Consequently, when the helicopter is being operated in the nap-of-the-earth flight regime, it is necessary for the pilot to cause the helicopter to emerge from its covert location from time to time to assess the battlefield situation and/or take other appropriate action and then to bring the helicopter back into a hidden position as soon as such action is completed. It will be appreciated that the degree of vulnerability of the helicopter to enemy threats increases dramatically with the time of its exposure, so that it is imperative that the amount of time for which the helicopter is exposed be limited to the required minimum.
This so-called bob-up/bob-down or unmask/remask maneuver is currently often being performed in response to appropriate manipulation of the collective stick by the pilot. Thus, the heretofore customary manual performance of this maneuver requires the pilot to make the correct collective stick input without exceeding power limits and to stabilize the helicopter at the desired altitude as rapidly as possible.
Even when the helicopter uses a model-following control system with a side-arm controller, it is difficult for the pilot to make the correct magnitude and duration inputs while avoiding controller cross-axis coupling. Moreover, the performance of this maneuver manually requires a great deal of attention on the part of the pilot and is extremely difficult to accomplish at maximum permissible rates of ascent and descent. As a result, the aircraft may be exposed to threats for an excessive amount of time. In addition, a large proportion of the pilot's attention is devoted to the performance of the bob-up/bob-down maneuver, which detracts from his ability to use the aircraft sensors, to evaluate threats, or to perform other mission tasks.
Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a aircraft flight control system which does not possess the disadvantages of the known systems of this kind.
Still another object of the present invention is to develop the control system of the type here under consideration in such a manner as to automate the performance of the bob-up/bob-down maneuver to the highest degree possible.
It is yet another object of the present invention to devise a helicopter flight control system of the above type which would minimize the extent of pilot's involvement in the performance of the bob-up/bob-down maneuver and thus permit the pilot to devote more of his attention to other tasks.
A concomitant object of the present invention is to design the control system of the above type in such a manner as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.